1. Field of the Invention
This invention relates to a method and apparatus for displaying a fluorescence image, wherein intrinsic fluorescence, which is produced from living body tissues when excitation light is irradiated to the living body tissues, is detected and displayed as an image representing information concerning the living body tissues.
2. Description of the Related Art
Research has heretofore been conducted with respect to techniques, wherein intrinsic fluorescence, which is produced by an intrinsic dye in living body tissues when excitation light is: irradiated to the living body tissues, is detected as an image, the image having been formed with the intrinsic fluorescence is analyzed, and a change in tissue condition of the living body tissues due to various kinds of diseases is discriminated in accordance with the results of the analysis.
At the beginning, research was conducted to determine a tissue condition of a living body by paying attention to a variation in intensity of intrinsic fluorescence produced from living body tissues. However, the intensity of the excitation light, which is received by the living body tissues, varies in accordance with a difference in an irradiation angle of the excitation light with respect to the living body tissues, a difference in a distance between an excitation light irradiating system and the living body tissues, and the like. Due to the difference in intensity of the excitation light, which is received by the living body tissues, the intensity of the intrinsic fluorescence produced from the living body tissues varies. Therefore, it has been found that, only with the information representing the intensity of the intrinsic fluorescence, sufficient capability of discriminating the tissue condition of the living body tissues cannot be obtained. Accordingly, there have been proposed, for example, techniques for discriminating a tissue condition of a measuring site by calculating a ratio of an intensity of intrinsic fluorescence, which is produced from a site of living body tissues when the site of the living body tissues is exposed to excitation light, to an intensity of the excitation light, which is received by the site of the living body tissues, i.e. by calculating a value reflecting a fluorescence yield, which value is not affected by the irradiation angle and the irradiation distance of the excitation light.
However, it is not always possible to directly detect the intensity of the excitation light, which is received by each site of the living body tissues. Also, if a distribution of the intensity of the excitation light, which has been reflected from the living body tissues exposed to the excitation light, accurately reflects the distribution of the intensity of the excitation light, which is received by the living body tissues, the distribution of the intensity of the excitation light, which is received by the living body tissues, can be determined by measuring the distribution of the intensity of the excitation light, which has been reflected from the living body tissues. However, of the excitation light irradiated to the living body tissues in order to cause the living body tissues to produce the intrinsic fluorescence, excitation light components having wavelengths on a short wavelength side within the wavelength region of visible light are not subject to uniform absorption by various living body tissues. Therefore, even if the distribution of the intensity of the excitation light, which has been reflected from the living body tissues exposed to the excitation light, is measured, the measured intensity distribution will not accurately reflect the distribution of the intensity of the excitation light, which is received by the living body tissues. Accordingly, as one of techniques for calculating the fluorescence yield, there has been proposed a technique, wherein near infrared light, which is subject to uniform absorption by various living body tissues, is employed as reference light and irradiated to the living body tissues, a distribution of an intensity of reflected reference light, which has been reflected from the living body tissues exposed to the reference light, is detected, and the detected distribution of the intensity of the reflected reference light is utilized in lieu of the distribution of the intensity of the excitation light, which is received by the living body tissues.
Also, a novel technique for discriminating a change in tissue condition of a living body has been proposed in, for example, PCT Japanese Publication No. 10(1998)-500588. With the proposed technique, a two-dimensional image signal, which has been obtained by detecting the intensity of reflected reference light having been reflected from living body tissues, is fed to a red-color channel of a color display device, and an image signal, which has been acquired by detecting the intensity of intrinsic fluorescence having been produced from the living body tissues, is fed to a green-color channel of the color display device. Further, the ratio of the intensity of the intrinsic fluorescence to the intensity of the reflected reference light (i.e., the fluorescence yield) is processed as display signals for altering the color and the luminance, and a change in tissue condition of the living body is displayed as an image.
However, the display luminance of the image formed by feeding the image signal, which has been obtained by detecting the intensity of the reflected reference light having been reflected from the living body tissues, to the red-color channel of the color display device, and feeding the image signal, which has been acquired by detecting the intensity of the intrinsic fluorescence having been produced from the living body tissues, to the green-color channel of the color display device is represented by complicated information comprising a mixture of luminance information, which reflects the shape, the distance, shadows, and the like, of the living body tissues to be seen, and luminance information, which reflects the tissue condition of the living body (i.e., the tissue condition concerning whether the living body tissues are cancerous tissues or normal tissues, and the like). Therefore, when the displayed image is visually seen, it is difficult to make a judgment as to whether a dark area in the image is the one due to a diseased part or the one due to a remote location, a concavity, or the like. As a result, the problems often occur in that the tissue condition of the living body, which is important information for diagnosis, cannot be discriminated correctly. Further, the problems often occur in that, since the intensity of the intrinsic fluorescence produced from a diseased part is low and the display luminance corresponding to the intrinsic fluorescence produced from the diseased part becomes low, a variation in color cannot be discriminated easily, and the presence of the diseased part cannot be found.
Furthermore, ordinarily, a dynamic range of an image displayed on a display device is narrower than the dynamic range of an image formed by a detecting device. Therefore, when the image formed by the detecting device is displayed on the display device, the problems described above are aggravated.
The primary object of the present invention is to provide a method of displaying a fluorescence image, wherein a tissue condition of a living body and a shape of the living body, which are information concerning living body tissues, are capable of being displayed accurately.
Another object of the present invention is to provide an apparatus for carrying out the method of displaying a fluorescence image.
The present invention provides a first method of displaying a fluorescence image, comprising the steps of:
i) irradiating excitation light and reference light to living body tissues, the excitation light causing the living body tissues to produce intrinsic fluorescence,
ii) detecting the intrinsic fluorescence, which has been produced from the living body tissues when the excitation light is irradiated to the living body tissues, and reflected reference light, which has been reflected from the living body tissues when the reference light is irradiated to the living body tissues, respectively as an intrinsic fluorescence image signal and a reference light image signal,
iii) forming display signals from the intrinsic fluorescence image signal and the reference light image signal, and
iv) displaying information concerning the living body tissues by utilizing the formed display signals,
wherein the display signals are formed such that an intensity of the reflected reference light is primarily reflected upon luminance, and a relative intensity of the intrinsic fluorescence is primarily reflected upon color.
In the first method of displaying a fluorescence image in accordance with the present invention, the reflection of the relative intensity of the intrinsic fluorescence upon color may be performed with an additive color mixture process conducted on the intrinsic fluorescence image signal and the reference light image signal.
The present invention also provides a second method of displaying a fluorescence image, comprising the steps of:
i) irradiating excitation light and reference light to living body tissues, the excitation light causing the living body tissues to produce intrinsic fluorescence,
ii) detecting the intrinsic fluorescence, which has been produced from the living body tissues when the excitation light is irradiated to the living body tissues, and reflected reference light, which has been reflected from the living body tissues when the reference light is irradiated to the living body tissues, respectively as an intrinsic fluorescence image signal and a reference light image signal,
iii) forming display signals from the intrinsic fluorescence image signal and the reference light image signal, and
iv) displaying information concerning the living body tissues by utilizing the formed display signals,
wherein the display signals are formed such that an intensity of the reflected reference light is primarily reflected upon luminance, and a pattern of a fluorescence spectrum of the intrinsic fluorescence is primarily reflected upon color.
In the second method of displaying a fluorescence image in accordance with the present invention, the reflection of the pattern of the fluorescence spectrum of the intrinsic fluorescence upon color may be performed by utilizing two kinds of intrinsic fluorescence image signal components, which are acquired from two different wavelength regions in the fluorescence spectrum of the intrinsic fluorescence.
The present invention further provides a first apparatus for displaying a fluorescence image, comprising:
i) irradiation means for irradiating excitation light and reference light to living body tissues, the excitation light causing the living body tissues to produce intrinsic fluorescence,
ii) detection means for detecting the intrinsic fluorescence, which has been produced from the living body tissues when the excitation light is irradiated to the living body tissues, and reflected reference light, which has been reflected from the living body tissues when the reference light is irradiated to the living body tissues, respectively as an intrinsic fluorescence image signal and a reference light image signal,
iii) display signal forming means for forming display signals from the intrinsic fluorescence image signal and the reference light image signal, and
iv) displaying means for displaying information concerning the living body tissues by utilizing the formed display signals,
wherein the display signal forming means forms the display signals such that an intensity of the reflected reference light is primarily reflected upon luminance, and a relative intensity of the intrinsic fluorescence is primarily reflected upon color.
In the first apparatus for displaying a fluorescence image in accordance with the present invention, the reflection of the relative intensity of the intrinsic fluorescence upon color may be performed with an additive color mixture process conducted on the intrinsic fluorescence image signal and the reference light image signal.
Also, in the first apparatus for displaying a fluorescence image in accordance with the present invention, the relative intensity of the intrinsic fluorescence may be obtained from a division of the intrinsic fluorescence image signal by the reference light image signal.
The present invention still further provides a second apparatus for displaying a fluorescence image, comprising:
i) irradiation means for irradiating excitation light and reference light to living body tissues, the excitation light causing the living body tissues to produce intrinsic fluorescence,
ii) detection means for detecting the intrinsic fluorescence, which has been produced from the living body tissues when the excitation light is irradiated to the living body tissues, and reflected reference light, which has been reflected from the living body tissues when the reference light is irradiated to the living body tissues, respectively as an intrinsic fluorescence image signal and a reference light image signal,
iii) display signal forming means for forming display signals from the intrinsic fluorescence image signal and the reference light image signal, and
iv) displaying means for displaying information concerning the living body tissues by utilizing the formed display signals,
wherein the display signal forming means forms the display signals such that an intensity of the reflected reference light is primarily reflected upon luminance, and a pattern of a fluorescence spectrum of the intrinsic fluorescence is primarily reflected upon color.
In the second apparatus for displaying a fluorescence image. in accordance with the present invention, the reflection of the pattern of the fluorescence spectrum of the intrinsic fluorescence upon color may be performed by utilizing two kinds of intrinsic fluorescence image signal components, which are acquired from two different wavelength regions in the fluorescence spectrum of the intrinsic fluorescence.
In the first and second apparatuses for displaying a fluorescence image in accordance with the present invention, the display signal forming means may be provided with a color matrix circuit. In such cases, the color matrix circuit may form R, G, and B signals.
Also, in the first and second apparatuses for displaying a fluorescence image in accordance with the present invention, the irradiation means may be provided with surface sequential irradiation means, and the surface sequential irradiation means may contain the irradiation means for irradiating the reference light.
The term xe2x80x9cdisplay signalsxe2x80x9d as used herein means the signals, from which a visible image is capable of being reproduced by the displaying means. By way of example, the display signals may be constituted of signals according to the NTSC method, signals according to the PAL method, signals according to the SECAM method, RGB signals, and the like.
Also, the term xe2x80x9crelative intensity of intrinsic fluorescencexe2x80x9d as used herein means the relative intensity of the intrinsic fluorescence, which does not depend upon the position of the living body tissues which position receives the excitation light, and the angle of incidence of the excitation light upon the living body tissues. By way of example, the relative intensity of the intrinsic fluorescence may be represented by the ratio of the intensity of the intrinsic fluorescence, which is produced from the living body tissues when the living body tissues are exposed to the excitation light, to the intensity of the excitation light, which is received by the living body tissues, i.e. may be represented by the fluorescence yield.
Further, the term xe2x80x9creflecting a pattern of a fluorescence spectrum of intrinsic fluorescence upon colorxe2x80x9d as used herein means both the cases where the pattern by itself of the fluorescence spectrum of the intrinsic fluorescence is reflected upon the color, and the cases where relative intensity representing a value representative of the spectral pattern at a specific wavelength region, or the like, is reflected upon the color. For example, relative intensity representing a value, which is obtained by dividing the intensity of the fluorescence spectrum over the entire wavelength region by the intensity of the fluorescence spectrum at a specific wavelength region, may be reflected upon the color.
With the first method of displaying a fluorescence image and the first apparatus for displaying a fluorescence image in accordance with the present invention, in which the information concerning the living body tissues is displayed by utilizing the display signals, the display signals are formed such that the intensity of the reflected reference light is primarily reflected upon a luminance signal constituting the display signals, and the relative intensity of the intrinsic fluorescence is primarily reflected upon chrominance signals constituting the display signals. In this manner, the intensity of the reflected reference light and the relative intensity of the intrinsic fluorescence are prevented from interfering with each other. Therefore, the tissue condition of the living body tissues and the shape of the living body tissues are capable of being displayed accurately.
With the first method of displaying a fluorescence image and the first apparatus for displaying a fluorescence image in accordance with the present invention, wherein the reflection of the relative intensity of the intrinsic fluorescence upon color is performed with the additive color mixture process conducted on the intrinsic fluorescence image signal and the reference light image signal, the information concerning the living body tissues is capable of being displayed more accurately.
With the first apparatus for displaying a fluorescence image in accordance with the present invention, wherein the relative intensity of the intrinsic fluorescence is obtained from the division of the intrinsic fluorescence image signal by the reference light image signal, the information concerning the living body tissues, which is obtained in accordance with the numerical value, is capable of being displayed more accurately.
With the second method of displaying a fluorescence image and the second apparatus for displaying a fluorescence image in accordance with the present invention, in which the information concerning the living body tissues is displayed by utilizing the display signals, the intensity of the reflected reference light is primarily reflected upon the luminance signal constituting the display signals, and the pattern of the fluorescence spectrum of the intrinsic fluorescence is primarily reflected upon the chrominance signals constituting the display signals. In this manner, the intensity of the reflected reference light and the intensity representing the pattern of the fluorescence spectrum of the intrinsic fluorescence are prevented from interfering with each other. Therefore, the tissue condition of the living body tissues and the shape of the living body tissues are capable of being displayed accurately.
With the second method of displaying a fluorescence image and the second apparatus for displaying a fluorescence image in accordance with the present invention, wherein the reflection of the pattern of the fluorescence spectrum of the intrinsic fluorescence upon color is performed by utilizing two kinds of intrinsic fluorescence image signal components, which are acquired from two different wavelength regions in the fluorescence spectrum of the intrinsic fluorescence, the information concerning the living body tissues is capable of being displayed more accurately.
With the first and second apparatuses for displaying a fluorescence image in accordance with the present invention, wherein the display signal forming means is provided with the color matrix circuit, more accurate display signals are capable of being formed, and the information concerning the living body tissues is capable of being displayed more accurately.
With the first and second apparatuses for displaying a fluorescence image in accordance with the present invention, wherein the display signal forming means is provided with the color matrix circuit, and the color matrix circuit forms the R, G, and B signals, the information concerning the living body tissues is capable of being displayed more accurately.
With the first and second apparatuses for displaying a fluorescence image in accordance with the present invention, wherein the irradiation means is provided with the surface sequential irradiation means, and the surface sequential irradiation means contains the irradiation means for irradiating the reference light, particular irradiation means for irradiating the reference light need not be provided. Therefore, the apparatus for displaying a fluorescence image is capable of being kept simple.